Why does Number constructor fail to parse numbers with separators?

Question

Since JavaScript has numeric separators (_, U+005F), why does Number("3_0") return NaN? Shouldn't it work like Number("0x08") which returns 8?

Number.isNaN(Number("3_0")) // true
Number.isNaN(Number(3_0))   // false
Number("3_0") === 30        // false
Number(3_0) === 30          // true

Answer 1

According to the spec, there are a few differences between the syntax accepted for numeric literals and the syntax accepted for a string value when being converted to a numeric value.

One of the differences is

A StringNumericLiteral cannot include a NumericLiteralSeparator.

If I have to guess, the reason is that accepting such characters would change the behavior of existing valid JavaScript code, which may break working applications.